The present disclosure relates to recording medium containing cassettes for containing sheet-like recording media, which are used in image forming apparatuses, such as digital photocopiers and laser printers, and image forming apparatuses including such a recording medium containing cassette.
A paper feed cassette (recording medium containing cassette) which is removably mounted in the body of an image forming apparatus has been commonly used. The paper feed cassette contains a stack of sheets of paper (recording medium). The paper feed cassette feeds paper to an image forming section in the body of the image forming apparatus in accordance with image forming operation, one sheet at a time. The paper feed cassette includes a paper support plate (recording medium support plate) on which a stack of paper is placed. The paper support plate is allowed to swing.
A typical configuration of the paper feed cassette will be described. FIGS. 8-10 are cross-sectional side views showing an example of a typical paper feed cassette 510. As shown in FIG. 8, the paper feed cassette 510 includes a paper support plate 528 on which a stack of paper 526 is placed. The paper support plate 528 is configured to be swung by a biasing member, such as a spring 532, so that a downstream portion in a paper conveyance direction (a right side of FIG. 8) thereof is moved upward and downward.
The stack of paper 526 placed on the paper support plate 528 of the paper feed cassette 510 is pressed against a pickup roller 529 which is provided on the apparatus body at a predetermined pressure which is exerted by the paper support plate 528 being urged upward by the spring 532. At this time, if a print start button of the image forming apparatus is pushed or switched on, the pickup roller 529 and a feed roller 530a of a feed roller pair 530 are driven to rotate in a direction indicated by an arrow in FIG. 8.
Typically, several top sheets of paper 526 placed on the paper support plate 528 are fed by the pickup roller 529 to the feed roller pair 530. The feed roller pair 530 includes the feed roller 530a and a separating roller 530b. The separating roller 530b is pressed against or withdrawn from the feed roller 530a. The separating roller 530b includes a torque limiter. Therefore, only when the rotational load exceeds a predetermined torque, the separating roller 530b is rotated by friction drive depending on the rotation of the feed roller 530a. Only the topmost sheet is separated by the separating roller 530b from the sheets of the paper 526 fed to the feed roller pair 530 and is then conveyed to a paper conveyance path 511. A trailing edge cursor 531 for evening or aligning the trailing edges of sheets of paper 526 is provided in a cassette base 525 and allowed to move along the paper conveyance direction (the left-right direction in FIGS. 8-10).
In the paper feed cassette 510, a limiting protrusion 525b for limiting the upward movement of the paper support plate 528 is provided on a wall portion 525a of the cassette base 525. Therefore, as shown in FIG. 9, when there is a large stack of paper 526, the limiting protrusion 525b presses the paper 526 so that the paper 526 and the paper support plate 528 are restrained from sticking out above the paper feed cassette 510.
During paper feed operation, the pickup roller 529 is rotated to feed the paper 526 while being situated in a lower position to press the paper 526. At this time, the paper 526 is pressed down by the pickup roller 529, and therefore, does not come into contact with the limiting protrusion 525b. Therefore, the skew of the paper 526 is reduced.
When there is a small stack of paper 526 in the paper feed cassette 510, as shown in FIG. 10, the inclination angle of the paper support plate 528 that is in contact with the limiting protrusion 525b is large. When there is no stack of paper 526, the paper support plate 528 reaches the maximum height. In this case, the paper support plate 528 sticks out above the paper feed cassette 510. Therefore, when the paper feed cassette 510 is inserted into or pulled out of the body of the image forming apparatus, the paper 526 and the paper support plate 528 touch the frame of the apparatus body. Note that if the size of the paper support plate 528 is reduced, the inclination angle of the paper support plate 528 increases, resulting in a higher maximum height of the paper support plate 528.